<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

    <script>

        var str = 'itbaizhan';
        console.log(str.indexOf('z')) // 5

        console.log(str.indexOf('a',7))

    </script>

</body>
</html>